This blog provides updated forecasts and comments on current weather or other topics

Sunday, January 9, 2011

Chances of Major Snowstorm Fading

One of the most difficult things about being a forecaster is maintaining objectivity.

Many of us got into the field because of a major storm event or a love of extreme weather. Like big snowstorms. And there is a tendency to forecast what you yearn for. Yes, we have our fancy models that provide objective guidance. But many times they disagree or have known biases, leaving some room for "professional judgment" and experience to make alterations. In some sense, meteorologists are the last people on earth you want to forecast the weather because we enjoy the major weather events so much. But eventually reality has to rule and this is such a case.

It is clear now that the trend of several of the forecast models is to bring the low and the associated warm air farther north and to move things in earlier. Yes, we might get some light initial snow but right now it looks like it will rapidly turn to rain near sea level.

Before discussing the mid-week event, I should note that our forecasts were pretty good for today, a mixture of rain showers near sea level over Puget Sound and snow showers in the convergence zone and over NW Washington is now occurring. Bellingham and environs has had 1-2 inches (see image at top). Bellingham and NW Washington is being helped along by northeasterly flow coming out of the Fraser River Valley (see surface plot below). Some snow has also fallen over the San Juans and northeast of Olympics such as near Sequim (no jokes about Sequim golfers and retirees in this post). And moderate snow is falling in the Cascades. The freezing level is around 700 ft right now and snow can push to the surface where the intensities are moderate.

OK, lets talk about the potential snowstorm. The type of event is different than the recent snowstorms of the past few years, which have been associated with convergence zones or disturbances coming out of the north. The midweek event was going to be an over-running snowstorm, in which cold air was in place and an approaching major Pacific system pushes moist over over the low level cold air, resulting in snow...and potentially lots of it. A great example of such an over-running snow event occurred during the last week of December 1996. In fact, there were two of them that week. At my house there was nearly 20 inches of snow on the ground by the end.

The issue with overrunning snow events is that many are associated with low centers and associated fronts. If the low goes too far south, you stay cold and dry. (meteorologists hate that!). If it goes north of us, we are warm, wet and often windy. To get massive snow, the low needs to go south of us, close enough to give us the precipitation but far enough to keep the warmest air at bay. And the low south of us helps pull nice cold BC air into the region. When this sets up right you can get HUGE snowstorms, but everything has to be perfect.

Several days ago the model solution looked very good for big snow...the low crossing the coast and staying near the Oregon/WA border. Major snows to the north over WA. And the fun did not stop there--more disturbances followed along a similar route. Big time snow. It might have been the end of KING-TV SnowMeister Jim Forman. At least he would need a second parka. As I noted in my previous post--there was considerable uncertainty in the solution and some major modeling systems (like the Canadian GEM model) were taking the low north of us.

During the last two days the main U.S. global model (GFS) has altered its solution . Precipitation comes in much earlier (early Wed morning) and the low moves farther north.

Let me show you. Here are several forecasts, starting at different times but all valid at the same time.

First a forecast of sea level pressure and temperature (shading,yellow is warm and blue is cold) for Wednesday at 4 PM for a forecasting starting Wednesday at 4 PM. Nice and cold, with the low well to the south.

Here is the latest forecast valid at the same time. See the difference? The low and associate warm front is way farther north.

In the latest runs, precipitation starts coming in late Tuesday...and yes, it could start as snow, but there would be a rapid switch to rain at low levels.

Here is the latest 24-h period snow forecasts. First the 24-h ending Wednesday at 4 AM. Up to six inches along the coast, over SW Washington and the mountains, but only a few inches at most near Puget Sound.

And here is the subsequent 24h ending Thursday at 4 AM. The influence of warmer air is obvious--only in the far northern portion of western WA is snow maintained. But the Cascades gets hammered and snow is king over eastern WA.

Again, there is uncertainty of the forecasts, but that uncertainty is dropping as we get closer to the event. Bottom line: most of you will see snow, but the huge event suggested few days ago appears much more unlikely. Also, be VERY careful when looking at forecasts more than 3-4 days out, particularly events where the exact location of weather features are critical.

32 comments:

While I love big snowstorms and am still keeping my fingers crossed, the NWS right up until 3AM today, was forecasting 3-6" here east of North Bend. We received maybe an inch and that's stretching it. Everyone was taken by surprise by the November event, and we ended up with 6" last week that was not forecasted. I am beginning to think that looking out my window is the only way to know for sure.

Cliff,We love reading your blog. We read it every time you post and always learn something. We're hoping to see the dramatic weather later this week, but see it's chances are diminishing as we get closer. Oh, well. Maybe there will be some shifts or changes that will give us another chance at it. Love the major events!Thanks for all your time.Candice

Darn. I had really been optimistic about this one. It seemed as though the models had almost all converged on the major snow event as of Friday.

I guess I will need to head to the mountains to get my snow fix instead. Then again, who knows? We're still a few days out, and I do live on the north end, smack in the middle of the PSCZ at around 500'. One can still hope?

I'm gonna play the wait and see game. These senarios look like it will change daily until the day of landfall. I personally would love to see the storm hit just south of Portland where I live right now, but would love to see my home town of Woodinville to get slammed.

How does the north end (Bham/Blaine/etc...) of NW WA look for the "warmer" end of your predictions? Would we still be close enough to the cold air throughout the 4-5 days that most all would be snow, or would we face a similar mix to the rest of WA? I know in previous events it's varied between seeing the same, to sometimes a 5-10 degree shift (which has caused us to get dumped on and the rest not to be touched)

The new runs look completely different now! Wow. I can see clearly why you can't get too excited that far out. The air mass right now isn't all that cold. There's a fine line between 39F and cold rain and 34F and wet snow. Thanks Cliff!

Well, the good news is this is the beginning of where La Nina really starts to affect us.Also, be careful what you wish for as we still have the rest of January, February and even March to see what pans out.

I think I would rather go with a 2-3 inch dump from a weak cold low dropping out of the north than bet the house on a southern stream mega snow event. The southern stream has crushed my soul loving snow hopes more than a few times. Now a potential week of sequential snowstorms and 850mb temperatures of -9 to -12 has turned into warm rain and +6 at times --- basically the exact opposite of a snowstorm. The GFS doesn't even have anything interesting through the extra long range now. It was surprising how fast the GFS changed course...almost over a single run yesterday.

I know it's redundant, but I want to echo the kudos of appreciation for your detailed explanations of what is happening, why it's happening, how the models do and don't work, how meteorologists work and think, and all the other incredible and incredibly useful information you are so generous in sharing.

This was on my Facebook news feed and I thought you'd enjoy it, Cliff:

Maria Shimizu Christensen

just suddenly hit me tonight that we live in a city where 3 of the most popular local celebrities are a meteorologist at the UW: Cliff Mass, a weatherman who isn't even a TV weatherman; a librarian: Nancy Pearl, who even has a Nancy Pearl action figure; and a kinda scruffy looking, wildly successful chef: Tom Douglas. That may say everything you need to know about Seattle.

I have lived here for about 35 years now, and I crave snow all the time. I have old video and audio recordings of TV and radio weather reports going all the way back to 1980. Virtually every single major weather event has been recorded, nowadays in HD on my Tivo. I am obsessed with snow. Imagine my disbelief when I saw all this talk of a historic snowstorm. I knew better deep down. I have lived through countless letdowns over the decades. It is almost a given that any major snowstorm we get will be a surprise event, not something forecast. It is also a given that any talk of a southern wet system is just talk. I don't recall this ever happening since I moved here in 1976, except for the Dec. 1996 storm, which doesn't even count since it warmed up right away. I want a prolonged sub-freezing cold spell lasting at least 5 days with only dry, cold blowing snow.

Snowing right now in Olympia. I have no faith in any forecasters or forecasting methods. If you want to know what the weather will be in Washington, step outside and look around. Looking at the satellite can give you an idea of what's coming in the next few hours, but even this is not accurate to any great degree.